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ELECTRIC CLOCK SYSTEM Oscar H. Dlcke, Rochester, N. Y., asslgnor to International Business Machines Corporation, New York, N. Y., a corporation of New York Original application December 14, 1938, Serial No. 245,700, now Patent No. 2,313,466, dated March 9, 1943. Divided and this application January 18, 1943, Serial No. 472,698

8 Claims.

The present invention relates to time control systems and more particularly to time clock systems driven by synchronous motors for punchin or printing on a time card the time of arrival and departure of an employee to and from his place of employment, indicating time in railway stations, schools and omce buildings, and the like.

In systems of the above type the secondary clocks may be corrected in the sixtieth minute, in that extreme accuracy in the last minute is not important.

In accordance with the present invention a slow secondary clock is advanced by a second or auxiliary synchronous motor which is connected to the time shaft by a gear train having a higher gear ratio so as to rotate the time shaft at a higher speed; or is corrected by the same motor by operating it at a higher speed from the same source of alternating current during the correcting period so as to make the time shaft run faster during correction of a slow clock. In accordance with the present invention a fast clock is corrected by stopping the secondary clock at a certain time indicating point and to again allow it to advance when the master clock reaches a corresponding time indicating point.

One of the objects of the present invention resides in the employment of one or more synchronous alternating current motors in each secondary clock and to correct such secondary clock without the use of costly relays, electro-magnetic setting means or the like, synchronous motors being less costly to build than relays.

Another object of the present invention is to render the secondary clocks very quiet not only during the clock advancing period but also during the clock correcting period.

Another object of the present invention resides in the provision of novel master clocks in which one element of the master clock used for operating clock correcting contacts is always in substantial synchronism with the secondary clocks in spite of the fact that the secondary clocks are at rest during alternating current cessation, such current being derived from a commercial power system having its frequency regulated to correctly manifest passing of time.

Other objects of the present invention reside in the provision of master clocks in which joint ,action of escapement mechanisms and synchronous motors driven by alternating current of regulated frequency correctly manifest the passing of time and in which the master clock time shaft is advanced in accordance with current cycle passage during the presence of alternating current.

Another object of the present invention resides in the provision of means to accelerate a master clock when it is tardy with respect to a synchronous motor and to retard such master clock when it is fast with respect to such synchronous motor during the presence of alternating current and to adjust its time measuring mechanism to normal during a cessation of alternating current.

'{lhe alternating current mentioned being derived from a source having its frequencyregulated to manifest accurately the passing of time.

Another object of the present invention resides in the provision of a plurality of line circuits connectin a master clock and one or more secondary clocks, these circuits being energized in sequence by contacts operated by the master clock, and to provide circuit selecting means for each secondary clock, which secondary clock has a high speed driving circuit and a low speed driving circuit, such that the high speed driving circuit is connected to the then energized line circuit when the secondary clock, is slow, but the low speed driving circuit is so connected when the secondary clock is correct. This means also acts to hold the secondary clock at stop when it is fast.

Other objects, purposes and characteristics and their advantages will appear from the following description when taken in connection with the drawings and from the drawings themselves in which:'

Fig. 1 shows a form of the invention in which the master clock comprises a time shaft driven during current presence by a synchronous motor and during current cessation by a normally braked escapement clock, and in which the secondary clock includes a time shaft driven by two different synchronous motors through gear trains having different gear ratio:

Fig. 1A shows how a. push button manually operated may correct a secondary clock;

Fig. 2 illustrates a modified master clock from that shown in Fig. 1 for controlling a secondary clock such as illustrated in Fig. '1, but through the medium of a single circuit, rectifiers being used to isolate two different currents into separate synchronous motors, and in which the master clock is automatically regulated from time to time so as to cause it to run in accordance with the rate of cycle passage only so long as there is no current cessation; and

Fig. 3 shows a two speed synchronous motor which constitutes either a two pole or a four pole to run in synchronism with alternating current I cycle passage, or by correcting a master electric clock in accordance with'the duration of a current cessation during each current cessation (Fig. 1). The secondary clocks may be used as tower clocks by using a separate unit for each dial, to operate record sheets, as bell ringers or 'for any other program purpose.

The inventions disclosed in this application are improvements over the inventions disclosed in my prior applications Ser. No. 365,584 filed May 23, 1929 now Patent No. 2,248,164 granted July 8, 1941; Ser. No. 441,109 filed April 2, 1930, now Patent No. 2,331,267 granted October 5, 1943; Ser.

Nos. 729,079 and 729,080 filed June 5, 1934, and now respectively Patent Nos. 2,248,165 and 2,185,334 granted respectivelyv on July 8, 1941 and January 2, 1940; Ser. No. 239,538 filed November 8, 1938, now Patent No. 2,359,973 granted October 10, 1944 and the application of Robert H. Dicke Ser. No. 39,146, filed September 4, 1935, now Patent No. 2,151,317, granted March 21, 1939. This applicationls a division of my prior application Ser. No. 245,700, filed December 14, 1938, now Patent, No. 2,313,466, granted on March 9, 1943.

It is also proposedto have secondary clocks of extremely simple construction. It is found that it is more economical to add an auxiliary motor than to add a relay, or an electrically operated clutch or gear shift. It is also proposed to employ contacts to temporarily stop the secondary clock by opening the motor circuit to correct a fast secondary clock.

' duction gearing including pinions I92, I94 and gears I93 and I95, the gear boxes G and G belng preferably oil filled. This reduction gearing preferably including sufficient friction or some worm gears, so that if the gear box is rotated and the synchronous motor whose rotor I96 projects from the gear box is not energized this rotor will be rotated at the same speed as the gear box, that is, will be stationary with respect to the gear box.

Referring to Fig. 1 the gear boxes G and G are pivotally mounted in stationary frames F F", F and F. To one end of these gear boxes is fastened a gear ill or I 40 which is preferably of slightly larger diameter than the gear box diameter. Concentric with and mounted within one of the bearings of the gear box is a motor shaft I4I or I4I on which is mounted the rotor I96 of a synchronous motor, these motors havins been designated SM and SM. Concentric with and mounted within the other bearing of the gear boxes G and G is a minute shaft (1 R. P. H.) designated I42 for the master clock and I42 for the secondary clock these minute shafts carry insulating cams K and K, respectively. The gear ratio of the pinions I92I94 and gears I93--I95 within the gear boxes G and Cl is such that if these gear boxes are held stationary and the synchronous motors SM" and SM are rotated at synchronous speed by current from the regulated frequency current source, the minute shafts I42 and I42 will rotate clockwise at a speed of one revolution per hour (1 R. P. H.).

The gear I40 of the master clock MC is at times, namely, during power failures, driven by any suitable escapement clock including preferably a pendulum I44 having a magnetic bob I44, an escape wheel I45, a driven pinion I46, and gear reduction means conver'ionally indicated by the pinions I46 and I48, and the gears I40 and I41. This escapement clock also includes a main spring I50 anchored to a hand Winding ratchet wheel I5I driving the gear I41. This ratchet wheel I5I is'kept from unwinding by the ratchet pawl I52 and may be hand wound by the key I53. Suitable electric motor winding means such as shown in my prior applications above referred to may be used if desired. The pendulum I44 is normally, that is when alternating current is available, held at rest, or is braked, by the electro-magnet I54I55 having its projecting legs surrounded individually by slugs or short circuited rings I56 of low resistance. The winding I55 of this electro-magnet is normally energized by direct current derived through the medium of a rectifier RI from the regulated alternating current source. The slugs or bucking coils I56 and the rectifier R1 are used to render the electromagnet slow-releasing. This slow releasing feature is employed to cause the escapement clock mechanism to drive the gear box G about its pivot for a slightly shorter time than the actual current cessation in order that the shaft I42 may accurately indicate standard time after a current cessation. In this connection it is desired to point out that a synchronous motor of the kind contemplated, and in fact any commercial synchronous motor, will coast for a time so that it will not be stationary during the entire current cessation. It has been observed that such a synchronous motor will, if deenergized for one second, be tardy only to the extent of about a half second. The slugs I56 are of such resistance that a current cessation of say two seconds will cause the two pole rotor I96 to coast thirty revolutions (onehalf second) and will cause the escapement clock to operate for one and one-half seconds.

Referring now to the secondary clock of'Fig. 1, the gear Hill is at times, namely when the secondary clock is being corrected, driven by an auxiliary synchronous or induction motor M through the medium of a gear train including pinions I51 and I58 and gears I59 and I40 The gear ratio of this gear train is preferably such that if the motor M having a rotor I66 is operated at normal speed and the synchronous motor SM is deenergized, the shaft I42 and cam K having a clock hand I9I indicated thereon, will be rotated at about sixty times normal speed, that is, at 60 R. P. H. instead of 1 R. P. H. The synchronous motor SM may drive the shaft I42 in exactly the same way as synchronous motor SM may drive shaft I42 Operation Fig. 1.Normally, that is when alternating current of regulated frequency is avail- I a able, the alternating current from the regulated source energizes the brake magnet Ill-Ill and holds the escapement portion of the master clock M at rest. At the same time the synchronous motor SM drives the shaft I42 and the'oam K at 1. R. P. H. through the medium of the gear reduction I92-I9i within the then stationary gear box G Also, this alternating current of regulated frequency flows through contacts IGIl-IGI through the line L through winding of synchronous motor SM", and through common return wire C back to the power line, and causes the shaft I42 and the cam K" to be rotated at 1 R. P. H. When the master clock cam K reaches the 59:00 minute position the contacts I80I6I open and the contacts ISO-I82 close. The secondary clock motor SM stops due to deenergization of line wire L and if the secondary clock was less than fifty-nine seconds fast the contacts I83I64 of the secondary clock will not yet have opened. The application of the regulated alternating current frequency to the high wire H causes the motor M of the secondary clock to be operated to cause the minute shaft (1 R. P. H.) I42 to be driven at about sixty times normal speed. This high speed rotation of the shaft Hi2 and cam K will, however, only continue until the contacts I63I84 operated by this cam K open. The secondary clock may therefore be slow as much as fifty-nine minutes and be brought to the end-of-hour position during the last minute of actual time as indicated by the master clock. When the master clock now reaches the end-of-hour or sixty minute position, the contacts ISO-482 open and the contacts I60-I6I reclose after which the secondary clock will run in exact synchronism with the master clock until the fifty-nine minute position of both clocks is reached providing there has been no currentcessation. If a current cessation occurs during a certain hour and it does not exceed fiftynine minutes the secondary clock will be corrected during the sixtieth minute of such hour. Obviously, if desired, corrections of longer outages than one hour may be corrected if the discs or cams K and K are driven by two hour or three hour shafts.

Fig. 1A illustrates how secondary clocks, such as shown in Fig. 1, may be manually corrected. Let us assume that a person has tuned his radio set to receive the usual Arlington or any other time signal audible over such set. He will depress the push button PB from one to several minutes before the end of the hour as a result of which all secondary clocks will assume the sixty minute or end-of-hour position. When he hears the sound manifesting the end-of-hour period he will release the push button PB as a result of which all secondary clocks will again be operated 'at normal speed and will be correct. A plurality fiers RI and RI and transformers T and T are really filtering apparatus so that it can still be said that the secondary clocks of Figs. 1 and 2 are identical.

Referring to the master clock of Fig. 2, this clock is an escapement clock in which the pendulum is not braked like it is in Fig. 2 of my patent No. 2,359,973 granted Oct. 10, 1944, but is conidentical to the secondary clock which has been shown very conventionally, there is preferably provided a permanent magnet PM which has leakage poles of soft iron ill projecting inwardly from the poles of the permanet magnet. It is also provided with soft iron extensions Ill. This permanent magnet is placed directly below the pendulum I12 having a soft iron bob I12- and the pendulum is then adjusted to keepcorrect time.

The leakage poles are provided with a sucking winding I18, so to speak, which is at times energized by direct current derived from the regulated alternating current system through the medium of a rectifier RI and flowing through the front contact I18 of relay R and the front contact I14 of the relay R The flow of this current is in such a direction through the winding II3that the magnetomotive force produced thereby aids the magnetomotive force of the permanent magnet and causes a large part of the flux emitted by said permanent magnet to be diverted away from the pendulum so that gravity is no longer magnetically aided to any appreciable extent and the pendulum operates at a lower frequency. In a similar manner the soft iron extensions III are provided with boosting windings I18 and I'll which when energized by direct current derived through the rectifier RI through the front contact I19 of relay R and the back contact I14 of relay R causes the apparent strength of the permanent magnet PM to be increased thereby still further magnetically aiding gravity and causing the pendulum to operate at a faster rate or frequency. The windings I13, I16 and Ill are when energized so poled as to aid the permanent magnet so as to avoid weakening of the permanent magnet as might be the case if they were bucking its magnetomotive force.

The relay R is so controlled that it is deenergized when the main spring I18 is especially fully wound up, that is, is wound up to a point where contacts I82-I83 open, as it would be if the escapement did not quite keep up with thesynchronous winding motor SM and when deenergized it speeds up the escapement clock for reasons above given. The relay R is however also deenergized when the contact I82 is dead by reason of being out of contact with the contact pin I80. This control of the relays R and R is accomplished by connecting the pin I88 electrically to the gear I8I, which in turn is connected by the brush I86 directly to the out-put side of rectifier R1 and by feeding either the spring contact I82 alone or both of the contact springs I82 and I83 with energy from this rectifier. The spring contact I82 is connected to relay R through the medium of a first slip ring and the contact I83 is connected to the relay R through the medium of a second slip ring by a wire passing through a hole in the first slip ring. If the main spring I18 is fully wound the contacts I 8Il-I82 are closed with contacts I82 and I83 still in engagement, thus energizing relays R and R but if the main spring is slightly over-wound because the escapement II2I I5 is running slower than the winding motor, that is, is running slower than the cycle passage of the alternating current, the relay R drops although the relay R remains energlzed, thereby causing the pendulum to be speeded up. Putting this in different words, after a temporary current cessation both of the relays R and R are in retracted conditions. When the main spring is fully wound the relays R and R 7 pick up and by closure of their front contacts I14 and H9 energize the sucking winding I13 thereby reducing from normal the downward pull on the pendulum I12. This causes the pendulum to run abnormally slow and causes winding motor SM", which was substituted for the winding motor SM when the relay R picked up, to gain with respect to the escapement "2-415, resulting in the opening of contacts l82l 83 and in the deenergization of relay R With the relay R now deenergized the boosting windings ITS-Ill are energized thereby causing the escapement to run a little fast resulting in picking up of relay B. This relay R therefore periodically picks up and drops to maintain the escapement in synchronism with synchronous motor driven winding apparatus. The worm wheels 228 and 229 and the worms 230 and 23! have such a gear ratio that the winding shaft 242 operates at exactly 1 R. P. H. when the low speed synchronous motor SM operates at synchronous speed from alternating current of regulated frequency and will operate at exactly 3 R. P. H. when the high speed synchronous motor SM operates at synchronous speed from the regulated source of alternating current. The gear ratio from main spring gear 18! to the shaft 233 is one to one, because gears l8l and 234 have the same number of teeth and pinions239 and 239 have the same number of teeth. In other words, when the pendulum I12 operates at correct speed and the winding shaft is rewound by the low speed synchronous motor SM the shafts 242 and 233 operateat the same speed of 1 R. P. H. The master clock MC also includes a rectifier R1 for at times'applying pulsating current of negative polarity to the secondary clocks.

Operation Fig. 2.-Under normal conditions, namely, when alternating current ispresent and when there has not been a current cessation for some time, the master clock MC is fully wound with the relay R energized and through its front contact I85 holds closed an energizing circuit for the low speed synchronous winding motor SM". The relay R will, of course, be at times energized and at other times deenerglzed to cause the escapement mechanism to run an average speed such that the contacts l82|83, for reasons already explained, remain at the point of barely touching. Between the zero and the fifty-nine minute position of the master clock as reflected by contacts l8l--i88-l89, and by clock hand l90,,pulsating current of positive polarity is derived from the regulated alternating current source through rectifier R1 and is applied to the line wire H L This current is blocked by the rectifier R1 but flows freely through the rectifier RI and energizes the transformer T The secondary winding of this transformer in turn has alternating current of the same frequency (60 cycle) induced therein, which alternating current energizes the synchronous motor SM".

The pulsating current of course returns to the,

source over the common return wire C As explained in connection with Fig. 1 the synchronous motor SM through gears I92l95 (see Fig. 1) drivesthe shaft I42 and the clock hand [9| exactly at the rate of 1 RP. H. when sixty cycle current of regulated frequency is applied thereto,

the gears l5'I-l58-l59 preferably having sumcient friction so that they will not be rotated by motor SM.

At the fifty-nine minute position of the master clock the contact I88 slips off of the cam K thereby causing contacts |8l-l88 to open. and

contacts l81-l89 to close. This results in the application of pulsating current of negative polarity to the line wire Il -L This current upon reaching the secondary clock is blocked by the rectifier R1 but flows freely through the rectifier RI and energizes the primary winding of transformer T The secondary winding of transformer T in turn energizes the synchronous motor M or an induction motor, through a circuit including contacts l63l64. This motor M drives the shaft I42 and clock hand I9l at substantially sixty times the speed they are driven by synchronous motor SM", so that the secondary clock may be driven to the sixty minute position where the contacts l63-l64 open to stop motor M. This occurs during the last minute of the hour as reflected by the master clock MC. That is, a clock that is slow to the extent of about fifty-eight minutes may be corrected. Also, a clock that is fast less than one minute will be corrected. At the end of the hour (sixty minute position) of the master clock'the contact I81 also slips off of the cam K as a result of which contacts l8l-l88 close and contacts I81- l89 open, so that the secondary clocks all start from the sixty minute position in synchronism and operate again at the normal rate. It is thus seen that a fast clock will be corrected and that even though a power failure of fifty-eight minutes occurs the secondary clocks will be advanced. Also, it willbe noted since both of the windings associated with the permanent magnet PM are deenerglzed during a current cessation and also during the rewinding operation that the master clock will during this time be adjusted to normal speed adjustment, and therefore will keep very good time. It should be observed that rewinding motor SM has two-pole characteristics whereas synchronous motor SM has six-pole characteristics. Therefore the main spring H8 is rewound at three times normal rate so long as A. C. power is available with the relay R assuming its deenergized position. The clock therefore operates unregulated only during one and onehalf times the duration of the current cessation. The indicating lamp I91 indicates when the secondary clock S is being corrected.

Fig. 3.C0'nstruction and operation.In Fig. 3 has been illustrated a two circuit two speed single stator single rotor synchronous motor 2SM that may be used for clock correcting purposes or may be substituted for motors SM and SM of Fig. 2.

This two-speed synchronous motor 2SM comprises two generally U-shaped stator cores 348 and 3M constructed of soft iron laminations. One pole, namely, the rearward pole with respect to the direction of rotation, of each of these U- shaped cores 34,0 and. 3 is bifurcated and provided with a shading coil 342 to cause such direction of rotation. The ends of the poles of these U-shaped cores 340 and 3 are rounded to leave a small uniform air-gap between them and the tempered steel rotor 345 and are so spaced as to constitute a four pole construction in which alternate poles are shaded for the same direction of rotation and so that the shaded portion of a shaded pole lies adjacent the other pole of the same core 340 or 34!.

If now these cores are so excited from a source of alternating current that adjacent poles of different cores have like instantaneous magnetic polarities we have a typical two-pole motor staor of which each pole belongs half to one core 340 and half to the other core 3 and which two poles each has a single shading coil to produce 9 clockwise rotation or a magnetic field. This twopole magnetic field rotating in a clockwise direction produces hysteresis torque in the rotor 345 tending to drag this rotor with it. As the rotor approaches its synchronous speed of 3600 R. P. M. the rotor due to the path across it of low reluctance and including the two spokes in series, having in multiple therewith two rim portions, locks in with this magnetic field, so that the rotor operates at 3600 R. P. M., assuming a sixt cycle alternating current source.

If now the stator cores 340 and 3 are so magnetically excited from such a source of alternating current that adjacent poles of different cores have opposite instantaneous magnetic polarities we have a four-pole stator of which two adjacent poles belong to one core member 340 and the other two poles belong to the other core member 34!. This four-pole magnetized structure has alternate poles. only shaded, that is, has either the north poles or the south poles shaded for clockwise rotation for a particular magnetic wave 01' a magnetic cycle. This fourpole magnetic field will of course rotate only at a speed of 1800 R. P. M. and will tend to drag the rotor 345 with'it. When the rotor 345 approaches synchronous speed it will lock in, so to speak, with this rotating magnetic field. This lockingin eiIect is produced by the four slots 348 out radially into the rotor 345 from the outside and causes the rotor to operate at 1800 R. P. M.

In order to increase the amount of alternating current flowing in the shading rings 342 and correspondingly increase the lagging magnetic flux produced thereby the pole pieces are .provided with extensions of magnetic material 340 and 34!. By looking at the stator structure of Fig. 3 it will be seen that if the stator is magnetized to produce a two-Dole magnetic field the usual shading is afiorded but that when the stator is magnetized to produce a tour-pole magnetic field only two of the four poles are provided with shading coils. This has been done purposely, because if the other two poles had been bifurcated and shading rings had been provided these additional shading rings would have produced harmful eilects when the magnetic structure is excited to produce a two-pole magnetic field, in that such additional shading rings would lie in the'middle of the unshaded portion of each of the two poles.

In order to produce two-pole or four-pole magnetization of the core structure 34ll--34I the core 340 is preferably provided with a plane he ical coil 34'! and the core 34! is provided with a helical coil 348-349 having a center tap 350. This center tap is preferably connected to one terminal of the coil 341 the other terminal of this coil 34'! being connected to the common wire in the particular system in which the motor 2SM is used. Each of the coils 341, 348 and 349 preferably has the same number of turns so that the magneto-motive force from pole to pole of the two cores 340 and 341 is the same irrespective of which of the two circuits is energized. It is thus seen that if alternating current is caused to flow from the wire low" to the wire "cmmon fourpole magnetization will result causing the rotor to operate at 1800 R. P. M., but if alternating current is caused to flow from the wire high to the wire common two-pole magnetization resuts, the magnetic polarities for four-pole magnetization and for two-pole magnetization of the core 34! having been illustrated by the solid letters N and S and the dotted letters N and S, respectively. Under normal conditions the motor 10 28M" will be energized to constitute a four-pole motor, but it will be energized to constitute a twopole motor when a secondary clock is to be advanced or a main spring is to be wound up at double speed.

If the motor ISM" is substituted for the wiring and motors SM" and SM" the wire 1ow" will be connected to front contact I35 or relay R, whereas the wire high" will be connected to back contact I of this relay. The gear ratio of the winding sears will remain the same but the time required for the rewinding to catch up will be increased.

Referring to the drawings it should be understood that the various inventions and the various forms illustrating the same general invention have been shown specifically in some instances for the purpose of explaining their principles of operation and not with any attempt of limiting them to this particular construction. Referring to Figs. 1 and 2, for instance, the two embodiments of master clocks illustrated therein, although they have been illustrated as master clocks and are particularly applicable to perform a master-clock function it should be understood that they may be used as a mantle clock of the sustained power type. In Fig. 1 the condenser N is used to dampen out the direct current ripples produced by the rectifier RI", so that the direct current flowing in the coil I55 is substantially continuous. In each form of the invention-illustrating a clock system two secondary clocks have been illustrated. One of these secondary clocks shows its outside appearance whereas the other shows conventionally its internal construction.

The two speed motor of Fig. 3 may be used in place of the rewind motors SM and SM" of Fig. 2. Having thus shown and described a number of embodiments of the present invention it is desired to be understood that the invention is not limited to these particular constructions except as demanded by the scope of the following claims.

What I claim as new is:

1. In an alternating current electric clock system, the combination with a secondary clock comprising a housing mounted for rotation about an axis, a shaft prolecting'from said housing rotatable with respect to said housing about said axis, reduction gearing in said housing, a first synchronous motor for rotating said shaft through the medium of said gearing without rotating said housing, a gear train, a second synchronous motor for rotating said housing and said shaft together through the medium of said gear train but at a diflerent speed, and means including a master clock for at times energizing said first synchronous motor and for at other times energizing said second synchronous motor.

2. In an alternating current electric clock system, the combination with a secondary clock comprising a housing mounted for rotation about an axis, a shaft projecting from said housing rotatable with respect to said housing about said axis, reduction gearing in said housing, a first synchronous motor for rotating said shaft through the medium of said gearing without rotating said housing, a gear train, a second synchronous motor for rotating said housing and said shaft as a unitary structure through the medium of said gear train but at a different speed, means including a master clock for at times applying energizing current to said first synchronous motor and for at other times applying energizing current to said second synchronous motor,

11 contacts included in series with one of said synchronous motors and means operated by said shaft for opening said contacts when said shaft assumes a predetermined chronological condition.

3. In an alternating current electric clock system, the combination with a secondary clock comprising a clock hand, of two gear reduction gear trains, a synchronous alternating current motor for driving said clock hand at a speed to substantially correctly manifest the passing of time through the medium of one of said gear trains, another alternating current motor for driving said clock hand ata relatively much higher speed through the medium of the other of said gear trains, contacts controlled by said secondary clock which are open only for a short time at the beginning of each rotation of said clock hand, a master clock, a source of alternating current of regulated frequency regulated to correctly manifest the passing of time, two circuits extending from said master clock to said secondary clock, a shaft for said master clock, and contact mechanism operated by said shaft to close one of said circuits including said alternating current source and said synchronous alternating current motor during the greater initial portion of each revolution of said shaft and for closing said other circuit including said source of alternating current, said contacts and said another alternating current motor during a final small portion of each revolution of said shaft, whereby said secondary clock is operated at normal speed during the greater initial portion of a unit of time and is operated at a relatively much higher speed near the end of said unit of time but only until said hand reaches its end of revolution position.

4. In an electric clock system, the combination with a source of alternating current having its frequency regulated to correctly manifest the passing of time; a master clock including means for rotating a shaft to correctly manifest the passing of time as determined by said alternating current and which means upon cessation of said current rotates said shaft to substantially correctly manifest the passing of time; a secondary clock including a time shaft, a time indicator rotated by said shaft, two gear trains for driving said shaft, two alternating current circuits, an alternating current synchronous motor for driving said time shaft through the medium of one of said gear trains at a speed to correctly manifest the passing of time when energized from said alternating current source, contacts operated by said time shaft and opened during an initial increment of a revolution of said time shaft, an-

, said clock hand and included in series with said another alternating current motor, and means for correcting said secondary clock effective to open the energizing circuit for said synchronous motor and closing the circuit for said another'alternating current motor before said clock-hand reaches the end of a revolution and for again opening the circuit for said another alternating motorat the point where it was closed by said last men tioned means and reclosing the circuit for said synchronous motor at the exact time as is manifested by said clock-hand when at the end of a revolution, whereby the said circuit for said another alternating current motor is actually opened at another point by said contacts when said clock-hand reaches its end-of-revolutijcn position.

6. In an alternating current electric clock system, the combination with a secondary clock comprising a housing mounted for rotation about an axis, a shaft projecting from said housing rotatable with respect to said housing and coaxial with said axis, reduction gearing in said housing, a first synchronous motor for rotating said shaft with respect to said housing through the medium of said gearing and without rotating said housing, a gear train, means including a second synchronous motor for rotating said housing, said gearing and said shaft in fixed relationship with each other and through the medium of said gear train but rotating said shaft at a different speed than when rotated by said first synchronous motor, and means for at times energizing said first synchronous motor and for at other times energizing said second synchronous motor.

7. In an alternating current electric clock system, the combination with a secondary clock comprising a clock hand, of two gear reduction gear trains, a snychronous alternating current motor for driving said clock hand at a speed to other alternating current motor for driving said time shaft at a relatively high speed through the medium of the other of said gear trains when energized by alternating current from said source,

with a source of alternating current having itsfrequency regulated to correctly manifest the passing of time; a secondary clock comprising a substantially correctly manifest the passing of time through the medium of one of said gear trains, an alternating current motor for driving said clock hand at a relatively much higher speed through the medium of the other of said gear trains, contacts controlled by said secondary clock which are open only for a short time at the beginning of each rotation of said clock hand included in series with said alternating current motor, two circuits extending to said secondary clock, a source of alternating current having its frequency regulated to correctly manifest the passing of time, and means for including said source in series in said circuits one at a time.

8. A secondary clock comprising, a housing mounted for rotation about an axis, a time shaft projecting from said housing and mounted for rotation with respect to said housing about said axis, time indicating means driven by said time shaft, reduction gearing in said housing, a synchronous motor for rotating said time shaft at a particular speed through the medium of said 13 reduction gearing without rotating said housing, a gear train, rhesus including an alternating current motor {or rotating said housini; said gearing and said time" shalt as a -unitary, structure and without operating said gearing with respect to said housing and through the medium of said gear train on; rotating said time shaft at a different particular speed; contacts included in series with said olterriating current motor, and nlreans driven by said ,iime shaft for opening when said time shaft asaumes a predetermined chronological condition.

OSCAR H. DICKE.

inn-masons crmn The Ioiioifing reierdices-are' of record in the tile 01 this intent:

Number Number 34 UNITED STATES PA'I EN'IB Name Date Bryce July 22, 1919 Warren June 24, 1930 Warren June 24, 1930 Bryce Sept. 6, 1932 Warren Mar. 26, 1935 Baumeister July 16, 1935 Warren Dec. 31, 1935 Poole Apr. 13, 1937 Harrison Dec. 7, 1937 Tallaferro Feb. 27, 1940 Pudeiko Mar. 5, 1940 FOREIGN PATENTS Country Date 3* Jan. 7, 1935 

